Coaches of rolling stock, such as tram trains, are of two main types. One type is equipped with double wheel units, one at each end of the coach. The other type, referred to as a trailing coach, has only one wheel unit located at that end of the coach which is not to be connected to another coach.
At the end or ends to be coupled together with a trailing coach, the coach has a fixed coupling device formed as a projecting beam with a vertically arranged socket intended to receive from above a depending shaft journal arranged at the outer end of an arm projecting in the longitudinal direction from the trailing coach end having no wheel unit. The depending shaft journal must be journalled in the socket to be able to make angular pivoting movements in the socket when the tram train or the like travels along curves, for example. With a rigidly supported shaft journal, impacts and vibrations occurring during travel, e.g. during braking, could cause damage to the rolling bodies and the race tracks of the rolling bearing used for journalling the shaft journal. To avoid such damages, it is essential to eliminate the transfer of such impacts, vibrations etc. This can preferably be accomplished by providing the coupling with elastic damping means arranged to absorb such impacts.
Furthermore, it is also important to provide the coupling with the possibility of certain relative movement about an imagined horizontal axis to allow travel over level differences without subjecting the bearing or the coupling means to stresses. Such adjustability can also, to a certain extent, be obtained with elastic damping means.
EP-A1-0 612 646 refers to a coach coupling as described above, wherein the depending shaft journal is supported in a deep groove ball bearing. The impact damping means in this case is designed as an elastomeric linkage having a stiff inner body with a vertical center bore for receiving the depending shaft journal, and a stiff outer body having a seat surface for the inner race ring of the ball bearing. The two stiff linkage bodies are spaced apart by a hemispherical elastomeric shell-formed body, and the two stiff linkage bodies have surfaces facing the shell-formed elastomeric body shaped to match the curvature of the "hemi-spherical" body. However, manufacturing such a linkage body is expensive and the design is partially open. Thus, the coupling must be protected from dirt and moisture by way of an external sealing bellows.